N-(perfluoroacyl)-N-phosphonomethyl glycine compounds, method of preparing same

ABSTRACT

N-(perfluoroacyl)-N-phosphonomethyl glycine compounds are prepared by the reaction of N-phosphonomethyl glycine with perfluoroacyl anhydrides employing an excess of the perfluoroalkanoic acid as the solvent. The N-(perfluoroacyl)-N-phosphonomethyl glycine compounds are useful as post-emergent herbicides and as sugar cane ripeners.

This application is a continuation-in-part of application Ser. No.580,252, filed May 23, 1975 now U.S. Pat. No. 3,970,695.

This invention relates to a process for producingN-(perfluoroacyl)-N-phosphonomethyl glycine compounds, to the compoundsproduced and to the herbicidal use thereof. More particularly, thisinvention relates to the preparation ofN-(perfluoroacyl)-N-phosphonomethyl glycine compounds by the reaction ofa perfluoroacyl anhydride with N-phosphonomethyl glycine in a solventconsisting of a perfluoroalkanoic acid. This invention also relates tothe post-emergent herbicidal use of theN-perfluoroacyl-N-phosphonomethyl glycine compounds produced.

N-acyl-N-phosphonomethyl glycine compounds are known as well as theiruse as herbicides. These acyl compounds are relatively weakpost-emergent herbicides. Their weak activity as herbicides is believedto be the result of the inactivating effect of the hydrolytically stableacyl groups replacing the nitrogen-bonded hydrogen of N-phosphonomethylglycine. In fact, it has been shown that when the N-benzoyl-; N-formyland N-acetyl derivatives of N-phosphonomethyl glycine are added to waterthere is no detectable hydrolysis whereas the perfluoroacyl derivativesare completely hydrolyzed within 24 hours.

In accordance with the process of this invention N-perfluoroacylderivatives of N-phosphonomethyl glycine are produced by forming anadmixture of N-phosphonomethyl glycine and a perfluoroalkanoic acid andthen adding thereto a perfluoroacyl anhydride and maintaining theresulting admixture at a temperature sufficiently elevated so as tocause said N-phosphonomethyl glycine and said perfluoroacyl anhydride toreact to produce the N-perfluoroacyl derivatives of N-phosphonomethylglycine. These derivatives have the formula ##STR1## wherein n is aninteger of from 1 to 4.

The compounds of formula I can then be treated with water to hydrolyzethe perfluoroacyl group attached to the --PO₃ group and replace thatperfluoroacyl group with a hydrogen.

The novel compounds of this invention have the formula ##STR2## whereinR is a H or ##STR3## AND N IS AN INTEGER OF FROM 1 TO 4.

The perfluoroalkanoic acids which are useful as the solvents for theprocess of the instant invention have the formula ##STR4## wherein n isfrom 1 to 4 and includes trifluoroacetic acid, pentafluoropropionicacid, heptafluorobutyric acid and nonafluoropentanoic acid. Without theuse of such solvents it has been found that the N-phosphonomethylglycine is not sufficiently soluble in the anhydride so that thereaction will take place. It is therefore considered that theperfluoroalkanoic acid solvent is essential to the process of thisinvention.

The perfluoroanhydrides which are useful in the process of thisinvention are those having the formula ##STR5## wherein each n is aninteger of from 1 to 4. For ease of reaction and ease of recovery of thereaction product, it is preferred that the n's have the same value andfurther the n of the perfluoroalkanoic acid also has the same value. Theperfluoroalkanoic anhydrides useful in the process of this inventioninclude trifluoroacetic anhydride, perfluorobutyric anhydride,perfluoropropionic anhydride and the like and mixedtrifluoroacetic-heptafluorobutyric;pentafluoropropionic-heptafluorobutyric anhydrides and the like.

In conducting the process of this invention the temperature should besufficiently elevated so as to initiate and sustain the reaction but notso elevated so as to cause undue decomposition of the reaction productor to produce side reactions. Generally reaction temperatures in therange of from about 20° C. to about 60° C. are preferred. It is evenmore preferred to conduct the reaction at temperatures of from 35° to55° C.

The weight ratio of the reactants can vary over side ranges. It is ofcourse apparent to those skilled in the art that one molecule of theanhydride reacts with one molecule of N-phosphonomethyl glycine toproduce the product. It is therefore preferred to employ at least onemole of the anhydride for each mole of the N-phosphonomethyl glycine. Itis even more preferred to employ from 0.5 to 3.0 moles of the anhydridefor each mole of the N-phosphonomethyl glycine, for ease of reaction andease of recovery of the reaction products.

The present process is generally conducted at atmospheric pressure.Although higher or lower pressure can be employed no commensurateadvantages are obtained thereby.

The N-perfluoroacyl-N-phosphonomethyl glycines of this invention areuseful as post-emergent herbicides and as sugar cane ripeners. Theprocess of this invention is particularly useful in the analyticaldetermination of and isolation of the metabolites of N-phosphonomethylglycine which contain a reactive nitrogen. The compounds produced by theprocess of this invention can be converted to alkyl esters employing adiazoalkane such as diazomethane, diazobutane, etc. and the estersrecovered by vapor phase chromatography. It has been found that thistechnique is useful where extremely small amounts of such derivativesare found.

In the following examples, which illustrate the invention, all parts andpercents are by weight unless otherwise indicated.

EXAMPLE 1

16.9 g. of N-phosphonomethyl glycine (0.1 mole) was placed in a flask.400 g. of trifluoroacetic acid (3.5 moles) was added in one portionfollowed immediately by the addition of 400 g. of trifluoroacetic acidanhydride (1.9 moles). The flask and its contents were stirredmechanically and warmed at 40°-45° C. for about 1 hour until ahomogeneous solution was obtained. The unreacted trifluoroacetic acidand anhydride were removed in vacuo at 50° C. to give 36.0 g. ofbis(N,O-trifluoroacetyl)-N-phosphonomethyl glycine having the formula##STR6##

The amorphous solid was analytically pure having the following elementalcomposition: Cal'd. %C, 23.6; %H, 1.5; %N, 4.1; %0, 31.1; %P, 8.6. Found%C, 23.28; %H, 1.68; %N, 3.88; %0, 31.57; %P, 8.58.

Analysis by nuclear magnetic resonance showed the product to besubstantially pure bis (N,O-trifluoroacetyl)-N-phosphonomethyl glycine.

EXAMPLE 2

13.5 g. of N-phosphonomethyl glycine (0.08 moles) was placed in a flask.400 g. of heptafluorobutyric acid (1.9 moles) was added in one portionfollowed immediately by the addition of 410 g. of heptafluorobutyricacid anhydride (1.0 mole) in one portion. The flask and its contentswere stirred mechanically and warmed at 40°-45° C. for about 5 hoursuntil a homogeneous solution was obtained. The unreactedheptafluorobutyric acid and anhydride were removed in vacuo at 40° C. togive 44.1 g. of bis (N,O-heptafluorobutyrl)-N-phosphonomethyl glycinehaving the formula ##STR7##

The amorphous solid was analytically pure having the following elementalcomposition: Calc'd. %C, 23.4; %H, 1.2; %N, 2.4; %O, 20.5; %F, 47.1; %P,5.4. Found %C, 23.54; %H, 1.08; %N, 2.50; %O, 19.96; %F, 47.40; %P,5.52.

Analysis by nuclear magnetic resonance showed the product to besubstantially pure bis (N,O-heptafluorobutyryl)-N-phosphonomethylglycine.

By following the procedure of Examples 1 and 2 but employingperfluoropropionic acid and perfluoropropionic acid anhydride oneproduces bis-(N,O-pentafluoropropanoyl)-N-phosphonomethyl glycine.

EXAMPLE 3

The post-emergence herbicidal activity of various compounds of thisivention is demonstrated as follows. The active ingredients are appliedin spray form to 14 or 21 day old specimens of various plant species.The spray, a water or organic solvent-water solution containing activeingredient and a surfactant (35 parts butylamine salt ofdodecylbenzene-sulfonic acid and 65 parts tall oil condensed withethylene oxide in the ratio of 11 moles ethylene oxide to 1 mole talloil), is applied to the plants in different sets of pans at severalrates (kg per hectare) of active ingredient. The treated plants areplaced in a greenhouse and the effects are observed and recorded afterapproximately 2 weeks or approximately 4 weeks, as is indicated in thelast column of Table I.

The post-emergence herbicidal activity index used in Table I is asfollows:

    ______________________________________                                        PLANT RESPONSE                                                                             INDEX    PLANT RESPONSE INDEX                                    ______________________________________                                        No injury    0        Severe injury  3                                        Slight injury                                                                              1        Killed         4                                        Moderate injury                                                                            2                                                                ______________________________________                                    

The plant species utilized in these tests are identified by letter inaccordance with the following legend:

A -- soybean

B -- sufar Beet

C -- wheat

D -- rice

E -- sorghum

F -- cocklebur

G -- wild Buckwheat

H -- morningglory

I -- hemp Sesbania

J -- lambsquarters

K -- smartweed

L -- velvetleaf

M -- downy Brome

N -- panicum Spp

O -- barnyardgrass

P -- crabgrass

                                      TABLE I                                     __________________________________________________________________________    COMPOUND                                                                             RATE A B C D E F G H I J K L M N O P WEEKS                             __________________________________________________________________________    I      0.224                                                                              1 0 0 0 0 1 0 0 0 0 --                                                                              0 0 0 0 0 2                                 I      1.12 1 1 1 0 0 0 0 1 0 1 --                                                                              1 1 0 1 1 2                                 I      1.12 0 2 1 0 1 1 1 1 0 2 --                                                                              1 2 2 2 3 4                                 I      4.48 1 3 3 0 1 1 1 2 1 2 --                                                                              2 1 4 2 3 4                                 I      4.48 1 4 3 1 3 2 2 2 1 3 --                                                                              3 3 4 3 4 2                                 I      11.2 2 3 3 3 3 3 1 2 2 3 --                                                                              3 3 4 4 4 4                                 I      11.2 3 4 4 4 3 3 2 3 2 4 --                                                                              4 4 4 4 4 2                                 __________________________________________________________________________

Compound I is bis-(N,O-trifluoroacetyl) N-phosphonomethyl glycine.

EXAMPLE 4

This example gives the procedure and results obtained by applying acompound of this invention to sugar cane.

In determining the appropriate rates and times to apply the compounds ofthis invention to sugar cane plants, it is necessary to consider boththe chronological age of the plant and its stage of maturity since cane,depending upon the practice in different geographical areas, is grownfrom 9 to about 30 months before harvest. Application at a rate of fromabout 0.1 to 5.0 pounds per acre can be made from about 2 to 8 weeksprior to the projected harvest date. Preferably, such applications aremade from 3 to 7 weeks before said date.

An active ingredient of this invention can be conveniently applied tothe plants as an aqueous solution or suspension. Said active ingredientcan, of course, be in its free acid form, or it may be employed in theform of an alkali metal or amine salt in order to improve such desirablefeatures as solubility or stability. For example, a liquid compositionmay be applied from a boom-spray, or a solid dust composition where theactive component is diluted with an inert solid such as clay can beflown on the plants from an aircraft. Suitable liquid compositionsinclude surfactants such as those enumerated in U.S. Pat. Nos. 3,224,865and 3,245,775. Preferred surface active agents which are convenient touse in liquid compositions of this invention are of the non-ionic typesuch as alkyl phenoxy poly(ethyleneoxy)ethanols, polyethylene oxideadducts of fatty and resin acids, and long chain alkyl mercaptan adductswith ethylene oxide.

A particularly preferred carrier for the acids or salts of thisinvention is water with about 0.1 to 2.0% by weight of surfactant addedthereto. Alternatively, the aqueous carrier can be replaced by anon-toxic mineral oil as such, or as an oil-in-water or water-in-oilemulsion. It has been found convenient to apply the compositions to theplants in the form of aqueous solutions, suspensions or emulsions, anddilution being such that a spray volume of from about 7 to 20 gallons ofliquid per acre will contain the desired dosage of active ingredient. Itwill be recognized, however, that higher or lower total spray volumescan be beneficially employed depending upon the particular dispensingapparatus and other factors well understood by those skilled in the art.

The specific tests which follow are presented as illustrative,non-limiting demonstrations of the useful and unexpected properties of anumber of representative compounds of this invention.

TEST PROCEDURE

0.5 Gram of a compound of the invention is dissolved in 4 ml. water thatcontains as a surfactant about 0.25% (w./w.) nonylphenol which wasethoxylated to contain about 10.5 mols. of ethylene oxide per mol. ofnonylphenyl ("Tergitol NPX"). 0.6 ml. of this solution is deposited ordropped by means of a syringe with a fine needle on the spindle area atthe top of the last visible dewlap of each of 20 stalks of sugar cane.(A dewlap is the junction between the blade of the leaf and the sheathwhich clasps the stalk). Ten of these stalks were harvested 4 weeksafter such treatment and 10 more were harvested 5 weeks after suchtreatment.

The top 15 joints of the treated cane as well as those of similaruntreated cane are removed, combined and analyzed in terms of juicepurity and pol percent cane, following the so-called "press-method"developed by T. Tanimoto, Hawaiian Planters Record, 57, 133 (1964). "Polpercent cane" is a polarmetric determination and equals the percentageof sucrose if the latter is the only substance in the solution whichwill rotate the plant of polarized light. In any event, determination ofthe pol percent cane is a standard and effective method for determiningthe sucrose content of sugar cane. The results of two separate tests Aand B are given below for the treated cane and for the untreated controlin each test. The compound employed is indicated by the example numberwhich describes its preparation.

    ______________________________________                                                    Four Weeks Five Weeks                                                           Juice    Pol %   Juice  Pol %                                   Treatment     Purity   Cane    Purity Cane                                    ______________________________________                                        Test A Example 1  75.39    9.52  75.19  9.24                                         Control    69.06    7.32  64.22  6.53                                  Test B Example 1  77.62    9.32  84.79  12.60                                        Control    75.36    8.28  75.73   8.64                                 ______________________________________                                    

In applying the compositions of this invention to the plants which it isdesired to control, it has been found to be desirable that the plant beemerged from the ground and even more desirable, that the plant be atleast at the two leaf stage for maximum effect. It has been found thatwhen the plants to be controlled have a portion of their growth abovethe ground or water, and the above-ground or above-water portion of theplant contacted with the herbicidal compositions of this invention atappropriate rates, the herbicide is translocated to kill such plantparts which are below the ground or water surface.

The phytotoxicant compositions, including concentrates which requiredilution prior to application to the plants, of this invention containat least one active ingredient of this invention, that is, anN-perfluoroacyl-N-phosphonomethyl glycine, and an adjuvant in liquid orsolid form. The compositions are prepared by admixing the activeingredient with an adjuvant including diluents, extenders, carriers andconditioning agents to provide compositions in the form offinely-divided particulate solids, solutions, dispersions or emulsions.Thus the active ingredient can be used with an adjuvant such as afinely-divided solid, a liquid of organic origin, water, a wettingagent, a dispersing agent, an emulsifying agent or any suitablecombination of these. From the viewpoint of economy and convenience,water is the preferred diluent, particularly with the highlywater-soluble glycine salts such as the alkali metal salts and amine andammonium salts. With these derivatives, solutions containing as high as0.6 kg. or more of active materials per liter can be readily prepared.

Generally the water containing herbicidal composition concentrates ofthis invention will contain from about 5 to 60 parts by weight activeingredient, from 0.5 to 10 parts by weight of a surface active agent andfrom 50 to 95 parts by weight of water, the total parts by weight of allconstituents being 100. These concentrates are usually diluted furtherwith water to provide sprayable compositions containing from 0.2 to 0.5kilograms per each 80 to 320 liter of solution in order that sufficientsprayable composition be available to adequately cover the areacontemplated to be sprayed with the proper concentration of activeingredient.

The phytotoxicant compositions of this invention preferably contain as aconditioning agent one or more surface-active agents in amountssufficient to render a given composition readily dispersible in water.The incorporation of a surface-active agent into the compositionsgreatly enhances their efficacy. By the term "surface-active agent" itis understood that wetting agents, dispersing agents, suspending agentsand emulsifying agents are included therein. Anionic, cationic andnon-ionic agents can be used with equal facility.

Preferred wetting agents are alkyl benzene and alkyl naphthalenesulfonates, sulfated fatty alcohols, amines or acid amides, long chainacid esters of sodium isotheonate, esters of sodium sulfosuccinate,sulfated or sulfonated fatty acid esters petroleum sulfonates,sulfonated vegetable oils, acetylenic glycols, polyoxyethylenederivatives of alkylphenols (particularly isooctylphenol andnonylphenol) and polyoxyethylene derivatives of the mono-higher fattyacid esters of hexitol anhydrides (e.g. sorbitan). Preferred dispersantsare methyl cellulose, polyvinyl alcohol, sodium lignin sulfonates,polymeric alkyl naphthalene sulfonates, sodium naphthalene sulfonate,polymethylene bisnaphthalenesulfonate, sodium N-methyl-N-(long chainacid) taurates and α-alkyl (C₁₂ C₁₈) omega-hydroxy poly(oxyethylene),the polyoxyethylene content averaging 3 to 20 moles; α(p-alkyl phenyl)omega hydroxy poly(oxyethylene) produced by the condensation of 1 moleof alkyl phenol with 6 moles of ethylene oxide; alkyl (C₈ -C₁₈) sulfate,ammonium, calcium, magnesium, potassium, sodium and zinc salts;α-hydro-omega hydroxy poly(oxyethylene) molecular weight 200-9,500;α-(p-nonyl phenyl) omega-hydroxy poly(oxyethylene) produced by thecondensation of 1 mole of nonyl phenol with an average of from 4-14 or30-90 moles of ethylene oxide; α(p-nonyl phenyl) omega-hydroxy poly(oxyethylene), 4-14 mole average polyoxyethylenes, mixture of dihydrogenphosphate or monohydrogen phosphate esters and the correspondingammonium, calcium, magnesium, monoethanol amine, potassium, sodium, andzinc salts of the phosphate esters; and amine salts of alkyl (C₈ -C₂₄)benzenesulfonic acid, butyl amine, dimethylaminopropylamine, mono anddiisopropylamine, mono, di, and triethanol amine.

Water-dispersible powder compositions can be made containing one or moreactive ingredients, an inert solid extender and one or more wetting anddispersing agents. The inert solid extenders are usually of mineralorigin such as the natural clays, diatomaceous earth and syntheticminerals derived from silica and the like. Examples of such extendersinclude kaolinites, attapulgite clay and synthetic magnesium silicate.The water-dispersible powder of this invention usually contains fromabout 5 to about 95 parts by weight of active ingredient, from about0.25 to 25 parts by weight of wetting agent, from about 0.25 to 25 partsby weight of dispersant and from 4.5 to about 94.5 parts by weight ofinert solid extender, all parts being by weight of the totalcomposition. Where required, from about 0.1 to 2.0 parts by weight ofthe solid inert extender can be replaced by a corrosion inhibitor oranti-foaming agent or both.

Although compositions of this invention can also contain otheradditaments, for example fertilizers, phytotoxicants and plant growthregulants, pesticides and the like used as adjuvants or in combinationwith any of the above-described adjuvants, it is preferred to employ thecompositions of this invention alone with sequential treatments with theother phytotoxicants, fertilizers and the like for maximum effect. Forexample, the field could be sprayed with a composition of this inventioneither before or after being treated with fertilizers, otherphytotoxicants and the like. The compositions of this invention can alsobe admixed with the other materials, e.g. fertilizers, otherphytotoxicants, etc., and applied in a single application. Chemicalsuseful in combination with the active ingredients of this inventioneither simultaneously or sequentially include for example triazines,ureas, carbamates, acetamides, acetanilides, uracils, acetic acids,phenols, thiolcarbamates, triazoles, benzoic acids, nitriles and thelike such as:

3-amino-2,5-dichlorobenzoic acid

3-amino-1,2,4-triazole

2-methoxy-4-ethylamino-6-isopropylamino-s-triazine

2-chloro-4-ethylamino-6-isopropylamino-s-triazine

2-chloro-N,N-diallylacetamide

2-chloroallyl diethyldithiocarbamate

N'-(4-chlorophenoxy) phenyl-N,N-dimethylurea

1,1'-dimethyl-4,4'-bipyridinium dichloride

isopropyl n-(3-chlorophenyl) carbamate

2,2-dichloropropionic acid

S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate

2-methoxy-3,6-dichlorobenzoic acid

2,6-dichlorobenzonitrile

N,n-dimethyl-2,2-diphenylacetamide

6,7-dihydrodipyrido (1,2-a:2',1'-c)-pyrazidiinium salt

3-(3,4-dichlorophenyl)-1,1-dimethylurea

4,6-dinitro-o-sec-butylphenol

2-methyl-4,6-dinitrophenol

ethyl N,N-dipropylthiolcarbamate

2,3,6-trichlorophenylacetic acid

5-bromo-3-isopropyl-6-methyluracil

3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea

2-methyl-4-chlorophenoxyacetic acid

3-(p-chlorophenyl)-1,1-dimethylurea

1-butyl-3-(3,4-dichlorophenyl)-1-methylurea

N-1-naphthylphthalamic acid

1,1'-dimethyl-4,4'-bipyridinium salt

2-chloro-4,6-bis(isopropylamino)-s-triazine

2,4-dichlorophenyl-4-nitrophenyl ether

alpha, alpha, alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine

S-propyl dipropylthiolcarbamate

2,4-dichlorophenoxyacetic acid

N-isopropyl-2-chloroacetanilide

2',6'-diethyl-N-methoxymethyl-2-chloroacetanilide2-chloro-4,6-bis(ethylamino)-s-triazine

monosodium acid methanearsonate

disodium methanecarsonate

N-(1,1-dimethylpropynyl)-3,5-dichlorobenzamide and giberrellin

Fertilizers useful in combination with the active ingredients includefor example ammonium nitrate, urea, potash, and superphosphate.

When operating in accordance with the present invention, effectiveamounts of the glycines are applied to above ground portions of plants.The application of liquid herbicidal compositions to above groundportions of plants can be carried out by conventional methods, e.g.power dusters, boom and hand sprayers and spray dusters. Thecompositions can also be applied from airplanes as a spray because oftheir effectiveness at low dosages. The application of herbicidalcompositions to aquatic plants is usually carried out by spraying thecompositions on the aquatic plants in the area where control of theaquatic plants is desired.

The application of an effective amount of the compounds of thisinvention to the plant is essential and critical for the practice of thepresent invention. The exact amount of active ingredient to be employedis dependent upon the response desired in the plant as well as suchother factors as the plant species and stage of development thereof, andthe amount of rainfall as well as the specific glycine employed. Infoliar treatment for the control of vegetative growth, the activeingredients are applied in amounts from about 0.0112 to about 25 or morekilograms per hectare. In applications for the control of aquaticplants, the active ingredients are applied in amounts of from about 0.01parts per million to about 1000 parts per million, based on the aquaticmedium. An effective amount for phytotoxic or herbicidal control is thatamount necessary for overall or selective control, i.e. a phytotoxic orherbicidal amount. It is believed that one skilled in the art canreadily determine from the teachings of this specification, includingexamples, the approximate application rate.

Although this invention is described with respect to specificmodifications, the details thereof ae not to be construed as limitationsexcept to the extent indicated in the following claims.

What is claimed is:
 1. A compound of the formula ##STR8## wherein R is amember of the group consisting of H and ##STR9## and n is an integer offrom 1 to
 4. 2. A compound of claim 1 wherein R is a ##STR10## groupingwherein n is from 1 to
 4. 3. A compound of claim 2 which isbis(N,O-trifluoroacetyl)-N-phosphonomethyl glycine.
 4. A compound ofclaim 2 which is bis-(N,O-heptafluorobutyryl)-N-phosphonomethyl glycine.5. A herbicidal composition comprising a herbicidally acceptablesurfactant, an inert diluent and a herbicidally effective amount of acompound of claim
 1. 6. A herbicidal composition comprising aherbicidally acceptable surfactant, an inert diluent and a herbicidallyeffective amount of a compound of claim
 2. 7. A herbicidal compositioncomprising a herbicidally acceptable surfactant, an inert diluent and aherbicidally effective amount of a compound of claim
 3. 8. A herbicidalcomposition comprising a herbicidally acceptable surfactant, an inertdiluent and a herbicidally effective amount of a compound of claim
 4. 9.A method of controlling undesirable plants which comprises contactingsaid plants with a herbicidal amount of a compound of claim
 1. 10. Amethod of controlling undesirable plants which comprises contacting saidplants with a herbicidal amount of a compound of claim
 2. 11. A methodof controlling undesirable plants which comprises contacting said plantswith a herbicidal amount of a compound of claim
 3. 12. A method ofcontrolling undesirable plants which comprises contacting said plantswith a herbicidal amount of a compound of claim 4.